Gavroche Thénardier (born 1820) is the only son of the Thénardier family. He is clever, street-wise, highly independent, and proudly stands up for those who need help. He is best friends with Cosette and his dog, Chou Chou, and the adoptive older brother of homeless children, Pressoir and Jurges (who are actually his unnamed siblings in the novel). He fights at the barricade with the Friends of the ABC, and is spared from death, unlike in the novel, when Chou Chou rescues him.

Gavroche is first seen as a baby, crying. Mme. Thénardier, annoyed by his crying, orders Cosette to babysit him while working, which she complies by taking a stroll down the path her mother took towards Montreuil-sur-Mer, singing her mother's lullaby while pushing Gavroche's stroller to a nearby tree. Three years later, Gavroche is seen throwing a live mouse onto Eponine's head offscreen, causing her and Azelma to scream and run off; he states to Cosette that bullying is wrong, which would reflect his later participation at the barricade.

The two children forge a very strong friendship, which includes Gavroche stealing food from the Inn to give Cosette while she is working, accompanying her on her trips to the local schoolhouse, church, and marketplace. The duo also eventually adopt a stray mutt they find in a field of flowers one day, which they decide to name Chou Chou. On Cosette's eighth birthday, Gavroche and Chou Chou search the entire night, and successfully find a potpourri sachet Eponine received from her mother that was originally a birthday gift for Cosette by Fantine. Earlier that day, Eponine showed off the sachet to her childhood crush, Toron, claiming her mother gave it to her, but was found out when Toron noticed a birthday note addressed to Cosette, and, out of embarrassment and jealousy, threw away the sachet while walking home from school.

On Christmas Eve, Gavroche is taken away to live and work for the local blacksmith, since the Thénardiers can no longer support four children, due to their lack of money from the now-deceased Fantine. The next day, Valjean takes Cosette away from the Thénardiers in Fantine's place, and while walking away from the Inn, the duo run into Gavroche and Chou Chou. Rather than going with them Gavroche states that he will stay in Montfermeil, since the blacksmith and his wife are kind, and would be upset if he were to leave all of a sudden. The two children share a bittersweet farewell, but Gavroche ensures Cosette that they will meet again sometime in the future.

Most notably, Gavroche is not killed from the gunshot he received on the barricade. Rather, he is saved by his childhood companion and dog, Chou Chou

The degree to which Gavroche and Cosette interacted is unknown in the novel, while in the Anime, they are very close friends

The two boys Gavroche "adopts" and calls his "younger brothers", Pressoir and Jurges, are actually his younger, unnamed siblings in the novel. None of them know their familial relationship in the novel, however